Curable coating compositions such as thermoset coatings are widely used in the coatings art. They are often used for topcoats in the automotive and industrial coatings industry. Color-plus-clear composite coatings are particularly useful as topcoats where exceptional gloss, depth of color, distinctness of image, or special metallic effects are desired. The automotive industry has made extensive use of these coatings for automotive body panels. Color-plus-clear composite coatings, however, require an extremely high degree of clarity in the clearcoat to achieve the desired visual effect. High-gloss coatings also require a low degree of visual aberrations at the surface of the coating in order to achieve the desired visual effect such as high distinctness of image (DOI).
As such, these coatings are especially susceptible to a phenomenon known as environmental etch. Environmental etch manifests itself as spots or marks on or in the finish of the coating that often cannot be rubbed out.
Coatings containing acrylic polymers crosslinked with aminoplast and isocyanate crosslinking agents are known to provide excellent etch resistance. However, melamine derivatives used as crosslinkers are highly functionalized and tend to yield localized regions of high crosslink density within the final cured film. To provide greater coating formulation latitude, it is more desirable to have a crosslinking component that allows adjustment of the number and distribution of potential crosslinking sites along the resin from which the crosslinking film is made.
It has been found that acrylamide compounds provide less functionalized crosslinkers and allow formulation of films ranging from hard films to flexible films. Cured films resulting from coating compositions of the present invention are unexpectedly highly etch resistant.